Wisconsin Islands Wilderness is a 29-acre federal wilderness area in Lake Michigan off Door Peninsula and Washington Island, made up of Spider, Gravel, and Hog islands and managed by the U.S. Fish and Wildlife Service. First protected around 1913 for migratory birds and designated wilderness in 1970, these low limestone and dolomite outcrops of the Niagara Escarpment remain uninhabited and are valued chiefly as nesting habitat. The islands support large colonies of herring gulls, double-crested cormorants, and other birds, including great black-backed gulls and Caspian terns. Because the breeding grounds are fragile, public access is prohibited and boaters must remain a quarter mile offshore.